The Master escapes from incarceration and allies himself with the
newly-awakened Sea Devils, the aquatic cousins of the Silurians, who have
also lain dormant for aeons in suspended animation. With an army of Sea
Devils at the Master's command as he seeks to conquer the Earth, the
Doctor soon realises that even with the backing of the British navy, there
may be no stopping his arch-foe this time.

Production

In planning Season Nine, Doctor Who producer Barry Letts and script
editor Terrance Dicks decided to include one serial which would be set on
or around the sea, something which had been done only rarely in the
programme's history. To write such a story, the production team turned to
Malcolm Hulke, who had most recently written Colony
In Space for Doctor Who's eighth season. It was decided
that the maritime adventure would see a return, of sorts, of the title
monsters from Hulke's Season Seven contribution The
Silurians. This time, however, Hulke would introduce an aquatic
version of the creatures; as such, “The Sea Silurians” was
commissioned in storyline form on March 29th, 1971, and as full scripts on
May 25th.

The story would also see the return of Roger Delgado as the Master. The
villain had featured in all five Season Eight adventures, but Letts and
Dicks now realised that this had overexposed the character, and decided to
restrict him to only a couple of appearances per year. “The Sea
Silurians” would therefore pick up where the Master's last story,
The Daemons, had left off and deal with the
villain's incarceration.

The Ministry of Defence was eager for the Royal Navy to
take part in a Doctor Who story

During Season Eight, Letts had been successful in securing the involvement
of the RAF for The Mind Of Evil, and so
decided to turn to the Royal Navy for support on “The Sea
Silurians”. Contacted in mid-June, the Ministry of Defence was eager
to take part so long as the Navy was cast in a positive light, offering
the use of men, equipment and locations.

It was realised that filming in naval locales would most comfortably be
carried out before the autumn weather became too chilly. However,
“The Sea Silurians” was planned to be the third story of
Season Nine (ensuring that there was an adventure set in outer space in
between each of the three based on Earth), suggesting a December or
January location shoot. Consequently, Letts decided to take advantage of
the long lead time between production and transmission afforded Doctor
Who since Jon Pertwee's debut and make “The Sea Silurians”
second as Serial LLL, while still maintaining its original place in the
season schedule. This would therefore be the first instance of a story
being made out of broadcast order in the show's history.

By mid-July, Hulke had changed the story's title to The Sea Devils.
He and Dicks had also made an attempt in the scripts to correct a
perceived error in The Silurians, namely the
impossibility of the title monsters actually hailing from the Silurian
period of Earth's prehistory (about 400 million years ago). Instead, they
now had the Doctor referring to the creatures as “Eocenes”,
but unfortunately the Eocene epoch (about 16 to 54 million years ago) was
barely more suitable, as it still came well in advance of the development
of mankind's very early ancestors.

The director assigned to The Sea Devils was Michael Briant, who had
previously helmed Colony In Space. Upon
arriving at Fraser Gunnery Range at HMS St George in Portsmouth,
Hampshire (the setting for scenes on the beach and at HMS Seaspite)
for the first two days of filming on October 21st and 22nd, Briant
realised that the outfits for the Sea Devils implied that they were naked.
Consequently, he had costume designer Maggie Fletcher dress the Sea Devils
in blue netting.

Briant's team returned to the Fraser Gunnery Range for one more day on
October 25th. On the 26th, the nearby HMS Reclaim, a diving
training vessel, served as its in-story namesake while the sea fort
sequences were performed at the No Man's Land Fort in the Solent, just off
the Isle of Wight. The sea fort setting was a late change to the scripts:
Hulke had originally written this material for an oil rig, but Briant was
unable to obtain permission to film on one.

Roger Delgado recorded all of his scenes despite being
notoriously afraid of the water

The rest of the location shoot then took place on the Isle of Wight
itself. On the 27th, Whitecliff Bay and Red Cliff, Sandown were the
venues for the sequences involving the shoreside minefield. Jon Pertwee
injured his ribs during recording when he dove forward and fell on the
sonic screwdriver prop, which was sitting in his breast pocket. October
28th saw cast and crew relocate to Bembridge Sailing Club and Bembridge
Harbour in Bembridge, for material at the quayside and at sea. Additional
beach shots were completed on the same day at Priory Bay, Seaview.
Location filming wrapped up on the 29th at Norris Castle in East Cowes,
which served as the prison. The conclusion of the exterior material came
as a particular relief to Delgado. Notoriously afraid of the water, the
actor had nonetheless persevered and recorded all the scenes that were
asked of him.

For the studio recording, Briant followed the usual Doctor Who
pattern of recording one episode per day. The first session took place on
Monday, November 15th and Tuesday the 16th, in BBC Television Centre
Studio 8. In episode one, the Master was shown watching The Rock
Collector, an episode of Clangers originally televised on April
25th. For part two, Briant himself provided the voice of the radio DJ. The
second studio block occurred on the 29th and 30th; the venue was again
TC8, although it was originally thought that TC1 would be employed
instead. TC8 was used once more for the final two studio days, December
13th and 14th.

To offset the expenses involved with the location filming, Briant opted
not to hire regular Doctor Who incidental music composer Dudley
Simpson, but instead have the score created in-house by a member of the
BBC's Radiophonic Workshop. John Baker was originally assigned to The
Sea Devils but after he fell ill, the duties were allocated to Malcolm
Clarke, whose unusual electronic score would prove to be one of the
serial's signatures.

Amusingly, on March 13th, two days after the transmission of The Sea
Devils part three, the Doctor Who office was visited by two
officials of the Ministry of Defence, who were concerned about footage in
the episode they believed was of a top-secret prototype submarine. It
transpired that the submarine was actually a model devised by visual
effects man Peter Day who, in an effort to make the prop look more
advanced, had accidentally included design features -- most notably
sleeker propellers -- similar to those the government was actually
testing.

Sources

Doctor Who: The Handbook: The Third Doctor by David J Howe and
Stephen James Walker (1996), Virgin Publishing, ISBN 0 426 20486 7.